1. Field of the Invention
The present invention relates to a rotary device and, in particular, to sealing reciprocating vanes of a rotary device.
2. Description of the Related Art
Rotary devices have long been thought to be an efficient way of rotating a shaft in the case of an rotary engine, pumping a fluid in the case of a pump, and compressing a fluid in the case of a compressor. Rotary devices are generally characterized by a rotating “piston”, or the equivalent, instead of a traditional linearly reciprocating piston as found in piston engines, pumps, and compressors. However, sealing the rotating “piston” has presented an extremely challenging problem, ultimately resulting in lack of widespread adoption of this technology. The sealing problems are particularly acute in a rotary engine as compared to a pump or a compressor. This is mainly because a combustion engine typically operates at higher pressures and temperatures, and therefore requires tighter sealing than in other applications. An inherent conflict in this technology is that tighter sealing may result in excessive friction and premature seal failure.
Many different approaches have been tried to address sealing issues with rotary devices including the elimination of seals altogether and reliance instead on close tolerances and accurate machining to seal leakage. Although in principle this approach may work for lower pressure and temperature applications, it is unsuitable for the higher temperatures and pressures of rotary engines where friction and thermal expansion are present. Ultimately the rotating “piston” will get hotter than the external casing. A “piston” that is a snug fit when the rotary engine has just been started will become tighter and tighter as it heats. A further complication is that unequal heating of the various parts will lead to non-uniform expansion of the parts, resulting in changes in shape as well as in size that make sealing attempts through tolerances and accurate machining unsuccessful in rotary engines.
Rotary engines have long been thought to be a viable replacement for the standard reciprocating piston engines. Rotary engines offer possible increases in mechanical and fuel efficiency, as well as more compact dimensions and a lower weight. The major deficiencies in traditional reciprocating piston engines arise from the short stroke of the pistons which leads to incomplete combustion. In theory, rotary engines provide a more continuous power stroke with decreased structural complexity, due mostly to the reduction in the number of moving parts. In practice, however, rotary engines have not received widespread acceptance and have only had limited success in replacing reciprocating piston engines, due mainly to the complexities involved in building a “simpler” rotary engine. Specifically, rotary engines typically involve a complex-shaped combustion chamber which presents problems in sealing the combustion chamber. The inability to adequately seal the combustion chamber has lead to many failed prototypes of the rotary engine.
One rotary engine that has received some commercial acceptance is the Wankel engine which is used in some models of automobiles produced by Mazda. A Wankel engine has a triangular shaped rotor, i.e., a rotating “piston” incorporating a central ring gear which is driven around a fixed pinion within an oval shaped housing. The triangular shaped rotor creates three combustion chambers between the rotor and the interior walls of the housing as the rotor turns within the housing. Each of the three rotating combustion chambers dynamically changes in volume as the triangular rotor rotates in the oblong housing and undergoes the four stages of the Otto cycle—intake, compression, ignition and exhaustion. The rotary motion is transferred to the drive shaft via an eccentric wheel that rides in a bearing in the rotor that matches the central ring gear. The drive shaft rotates once during every power stroke instead of twice as in a typical four stroke reciprocating piston engine. The Wankel engine promised higher power output with fewer moving parts than the Otto cycle reciprocating piston engine, however, technical difficulties associated with sealing the three rotating combustion chambers have apparently interfered with widespread adoption.
Another type of rotary engine is known as the axial vane rotary engine. In an axial vane rotary engine, a circular rotor is located between two cams, each cam having a cooperating undulating cam surface facing the rotor. The rotor has a series of angularly spaced apart slots to receive respective ones of axially sliding vanes whose ends reciprocatingly contact respective ones of the undulating cams surfaces so that combustion chambers are dynamically formed between adjacent axially sliding vanes. Axial vane rotary engines are described in U.S. Pat. Nos. 4,401,070, 5,429,084, 5,509,793 and 5,551,853, all of which are herein incorporated by reference.
An axial vane rotary engine has the capacity to provide greater output than a Wankel rotary engine of the same size. However, an axial vane rotary engine presents a greater sealing challenge since the vanes slide both axially with respect to the rotor and circumferentially with respect to the cam surfaces. The present invention is directed to a rotary device of improved design over the prior art which facilitates the ability to adequately seal the combustion chambers formed between adjacent vanes.
It is understood that one of skill in the art of rotary devices can apply the principles discussed herein in the various embodiments equally to other rotary devices such as pumps, compressors, expanders, etc.